Gas turbine power plant having auxiliary turbine driven by fuel gas being supplied to the combustion chamber



H. PFENNINGER June 3, 1952 GAS TURBINE POWER PLANT HAVING AUXILIARY TURBINE DRIVEN BY FUEL. GAS BEING SUPPLIED TO THE COMBUSTION CHAMBER Filed April 2, 1947 2 SHEETS--SHEET l m0 mmtoxm June 3, 1952 H. PFENNINGER 2,599,480

GAs IUPBINE PowER PLANT HAVING AUXILIAPY IUREINE DRIvEN BY FUEL GAs BEING SUPPLIED To THE coNBusTIoN CHAMBER Filed April z, 1947 2 SHEETS- SHEET 2 I N VENTOR .A AAW @www Patented June s, 1952 GAS TURBINE iBOWER PLANT. AH'AyINGr .AUX-1 ILIARYf vTIERBIINTE' 1 DRIYEN BY FUEL. GASY- BEING SUPPLIED TO T-HE. COMBUSTION CHAMBER.,l

Power lplants operatedA on compressed' gas; are already lenownfy in--wliich theA combustion chamber orf-the,` gas producer is operatedat the-pressure off the :fuel 'gas or` the air or' bothI considered togather: These-mediums may be corn-pressed'at thev place where the combustion takes place, but it: isalso possible-t0 cond'uctthe vfuel gasv in an already' compressed state to thev place whereit' is to be`A consumed. The iirstmetliod; for: example,

is*` utilized in' steamv producing-plants that areb fired" ywith compressed gas or-in heat enginesdriven directly' by" compressed gas, whereas the lattermethodis usually` employed. in power plants operated on natural gas.

The presentinvention, in contrastthereto; deals' with ia' power plant operated'A by compressedl gas under` conditions-where the pressure` of thel fuel gas vsupplied to' the p1ant is greater than that which is` required orv necessary in the combustion chamber of the power plant. The gas',v for ex'- axnple natural gas' as. obtained in nature, issues from theearthfat a much higher pressure than4 tlat at; which,` when' suitablyV stored, vit is to' be. used in' a4 heat engine plant. This is a situation usually' encountered" in` the chemical industries,4 erg'. in petroleum recovery Work whereefforts are madeto utlizenatural gas for the productionv of power'. The natural gas obtainedas' a byeprod-A uct-1in'petroleum'recoveryH operations is' often available under'high pressure (upto 60"-'atmos--'v pheresla Ifv itis desired-tof burnthis ga'sycon` tei'nin'gf up to' 80% of` methane, inA the furnaceo a.power plantiit must first bereducedi-to the pressuresusually` employed in the furnace; If'A the powerffplant' isdriven forv example by -afgas' turbine; the pressure inthe combustion chamber'- of such gas:turbine.is-usually notgreater than 3' to@ l2 atmospheres. The. pressurer of the-fuel gas must therefore be-- reduced-itc this'Y pressure. 'If' the@ fuel'z gas isi throttled dow-n, a large: portion of the. potential energy contained therein becomes losti.;`

The present-V invention relates to an apparatus:

forv solvingf this problem-, 'In accordance with the inveriion',l such1 gas.. priorto being burned-in thery combustion chambenofi a poweru plant-is first?v expanded: tof reduce its. pressure down tor the pressure said; combustion'. chamber, thisl bengfA effected: infan expansion. engin@v interposed? ahead of said combustion chamber. In this: manner the :great pressurergradienb inherent in thefnatural-,gas may once and for'v allv be broughtl effectivelyavdown to; the degree suitable forA permitting explcitation.v of energy in: the` power; plant;mense-A However. since-gases suon asfnatz- Aturbine power plant.

natural gas to theY aforesajdiilow pressures is;

uraligasissue: fromltheiearthY at a temperature ofil as; low--asY 20?"tof 40'5 Ci, theybecomeifintensely' cooled whenn subiectedttosuch 1expansion1 andathe. icev formed' asl aconsequencelrthereof :is: anti-to., interrupt theKL operation ofy thel expansion engine.l interposed: aheadrof -the-power-plant'.. It@is'there` fore'- preferable. to'A heat suoli gases; prior. to: effect@y ing their.;I expansion. The waste exhaustgases ofVl` the-power' plant are preferably utilzedforfrthis.:

purpose.

Figs; 3f-and- 4- are-'central' sections illustrating' modiedl constructions for the auxiliary turbine;- Referring nowto the drawingsnandiparticua larY to Figs. 1i and-'72,. the improved power-planteleseento` include a gas turbine elementi, a @com-`r pressm" `2r a' 'main electrical power generatoirf,v

anr'auxili'ary dynamoeleotricmachine which mayservev asA` an exciter for generator 3'* or-as a starter motor for the gas' turbineand compressor' units, ancla-nY expansion engine 5*in-tleV formL of a vgas turbine, allI offthesef components being'arV ranged axially in 'lineanddriven bin-or driving;v asthe" case vmay be,- acommonshaft6.-` The? combustion chamber' for --the gas Vturbine l isdesignated by'numeral- "l, and the natural gas.' prior to `its combustion inl combustion---chamberl of" theI power plant?,4 is' expandedin the; gastur:- bine 5- from-sits*` initially high pressure toY the pres*- sure prevailing inandfrequiredwby"combustionchamber 1. Y

The-naturali 'gast which may issue from-the' interiory off -thewea'rth at a veryvhigh pressure ofabout `60'atmospheres, for' exa-triple'y is supplied'y by pipe 8. Thecombustionvchamber'l isfusuajllyf operatedv at apressure of' -3 to v12"atmospheres; produced byv the air compressor 2"`o` the gas The expansion of..,tl`ie` effected in the gas. turbine ljinterposed, ahead. of the power plant per se, said' gasturbine bef- .ing Vdirectly supplietibyl the nautral gas. The

the turbine 5 from causing the already low temperature of the natural gas (20 to 40 C.) to drop below the dewpoint and hence cause breakdowns due to the formation of ice in the turbine, it is preferable to heat the natural gas in a preheater 9 by means of the exhaust gases from the turbine I before initiating its expansion. The exhaust waste gases from the gas turbine I, after passing through the preheater 9, are then allowed to escape into the atmosphere. Preheating of the natural gas also serves to increase the expansion eficiency of the turbine 5 interposed ahead of the power plant and further serves to assure the proper gas temperature that is required for effecting com-bustion in the combustion chamber 1. Regulation of the quantity of fuel gas required is preferably effected by causing the fuel inlet valves I of the expansion turbine to regulate the quantity of fuel gas in accordance with the load. While various types of governors may be adopted to automatically regulate the fuel inlet valves I0 in accordance with the load so that the rate of the fuel flow .will increase with an increase in load and vice versa, the preferred arrangement, and which is illustrated schematically in the drawing, operates on hydraulic principles. The governor system includes an oil pump I6 driven from a power take-off from shaft 6 and which delivers oil at substantially constant pressure to a distribution line I'I, an oil escape valve II in the distribution line I'I, and a ball type governor I8 driven at load speed and which regulates the rate at which oil is permitted to escape throughvalve II. The greater the discharge rate through valve II, the lower the oil pressure in line I'I and vice versa. Line I1 extends to the valves IU at the gas inlet side of the auxiliary turbine 5. These valves are conventional in construction, being spring loaded to a closed position and opened by a counter force variable with the oil pressure in line I1. Thus the greater the pressure in line I1, the greater will be the valve opening and vice versa. Operation of the governor system should now be quite obvious. If, for example, the plant load should increase, the speed of the output shaft 6 would tend to drop oif. This results in a movement of the gate I Ia in valve I I to the right thus reducing the rate at which the oil escapes through the valve, which is reflected as an increase in pressure in the oil line I'I at valves IU. Thus the valves I0 move to a new and more open position with the result that the rate at which the fuel flows through the auxiliary turbine 5 and to the combustion chamber 'I is increased and hence produces the required increase in power necessary to meet the new increased load condition. In the event that the plant load should decrease, which would be reflected by a momentary increase in speed, the opposite effect would take place and valves I would be caused to move toward a more closed position and thus reduce the rate of fuel flow through the auxiliary turbine 5 and into the combustion chamber 1. Regulation of the quantity of fuel gas by means of the inlet valves of the expansion turbine serves substantially to avoid any losses such as would be caused by throttling the gas and which losses for example would result if the quantity of fuel gas supplied were to be regulated by means of throttling devices associated with the combustion chamber of the power producing engine per se.A

Iny the interest of preventing any damage to the apparatus should the speed reach a dangerously high level an emergency fuel cut-off is provided. Concerning the latter, it will be observed from the drawing that oil pump I6 delivers pressure oil not only to the main distribution line I'I of the main governing system described above but also to an auxiliary distribution line Ha of the emergency cut-off system which latter is comprised of an emergency trip governor IIb and a cut-off valve IIla the operation of which is controlled by the oil pressure acting against a spring loaded piston IUb, and which valve is interposed in the fuel conduit 8 ahead of the fuel valves I0 on turbine 5.

Diaphragms for adjusting the respective oil pressures in the main and emergency distribution systems are indicated by reference numerals I Ib and I'Ic. A check valve, interconnected between the two systems and allowing a ow of oil from the main governing system into the emergency cut-off system in the event of high over-speed but never allowing any flow in the opposite direction is shown at I'Id. The emergency cut-off system operates as follows:

During normal operating conditions, the oil pressure in the emergency cut-off System remains practically constant and is approximately as high as the oil pressure at the outlet of pump I6 'whereas the oil pressure in the main governing system will fluctuate in accordance with the load, as previously explained, and is always lower than the pump pressure due to the variable bleeding action of valve IIa. Hence under such conditions, the emergency valve Illa will be maintained in its open position thus allowing free ow of the fuel gas to the fuel regulating valves IU. Should, however, the speed of the power plant rise above a selected maximum safe value, the emergency trip governorl IIb will then operate to allow free escape of oil therethrough thereby dropping the pressure in the emergency oil system I'Ia to practically zero which then permits the spring loaded piston I0b to move valve I0a to its fully closed position, thus shutting off the flow of fuel to turbine 5 and combustion chamber 1. Furthermore, the oil pressure in the main governing system being now momentarily higher than that in the emergency cut-01T system, the check valve IId allows a flow of oil from the former into the latter causing the governing oil pressure to likewise drop to zero and all the regulating valves ID likewise move to a fully closed position. By thus doubly obturating fuel admission to turbine 5, a high degree of safety is obtained.

As illustrated it is preferable to couple the expansion engine 5 directly with the shaft 6 of the main power plant components and hence also to use turbine 5 as a starter for the combustion gas turbine plant. Due to the short starting period involved, it is usually unnecessary to preheat the fuel gas prior to effecting its expansion since the heat retaining capacity of the constructional materials of which the expansion turbine is built will, during such starting period, adequately serve to prevent excessive cooling and the formation of ice consequently thereon.

It is preferable, during the rst stage of the starting procedure (i. e. while the gas turbine plant, driven by the expansion of the high pres-- sure fuel gases in turbine 5, runs up to about 25 percent of its normal speed), to exhaust the expanded fuel gases discharging from the said expansion turbine directly into the atmosphere through two-way valve I2, so that no accumulation of explosive gases will be formed in the combustion chamber I. After that, the flow of gas may be directed to combustion chamber I by turning valve I2 to the position shown in the drawing, and after the high pressure gas stream has been ignited, the plant will run up to full speed on account of the joint action of the driving energy gained from turbine 5 and that gained from turbine I.

In case it should be desired during the starting procedure to feed the fuel gas in preheated condition to the turbine 5 that serves as the power plant starter, a small combustion chamber I3 can be installed ahead of the fuel gas preheater 9 in the outlet pipe of main gas turbine l and fuel gas fed to this auxiliary combustion chamber I3 from the natural gas pipe 8 via an injector I4 'that supplies air for combustion, the air being drawn in by suction by the gas passing through the injector. The burned gas-air mixture vis conducted from the auxiliary combustion chamber I3 to the preheater 9.

It is not desirable to heat the natural gas ahead of the expansion turbine 5 as by direct combustion thereof, since, for that purpose it would be necessary to compress the combustion air to the same pressure as that of the natural gas and this would require a separate air compressor adapted to compress the air to the high pressure possessed by the gas. In addition, such an arrangement would require an extraneous source of power.

In order to prevent leakage of the expanded gases from the shaft seal of the expansion turbine 5, the latter may be constituted as a single bearings structure 5 as shown in Fig. 3 so as to preclude all possibility of leakage at the in let end of the turbine rotor. At the outlet end of the rotor, the pressure of the gas, during the starting period, is approximately equal to that of the ambient surroundings so that the danger of leakage is small if the shaft is well sealed. It is also possible to use an expansion turbine 5" as shown in Fig. 4 having a diffuser 2|' at the outlet of the turbine rotor blades adapted to keep the pressure at the shaft seal even lower than the atmospheric pressure. If the pressure drop in the expansion turbine is suitably moderate, a single crown impulse rotor may be used, as illustrated in Fig. 3. In such cases the gas pressure in the rotor casing at the inlet end of the turbine rotor would also, during they starting period, be approximately equal to the atmospheric pressure. As soon as the combustion gas turbine I has been started, the blower 2 serves to supply sealing air for all of the shaft seals 20 through pipe 2I.

I claim:

1. In a power plant, the combination comprising a main gas turbine, a compressor mechanically coupled to said turbine, a combustion chamber, the outlet of said compressor being connected to said combustion chamber, and the latter being connected to the inlet of the main turbine, an auxiliary gas turbine mechanically coupled to said main turbine and compressor, adjustable valve means at the gas inlet to said auxiliary turbine for controlling the gas flowing through said turbine from a source of gaseous fuel having a delivery pressure higher than the operating pressure of said combustion chamber, pipe connections between the outlet from said auxiliary turbine and said combustion chamber, valve means in said pipe connections for selectively exhausting the fuel gas to atmosphere to facilitate plant starting by said auxiliary turbine, and means responsive to plant load for adjusting said gas inlet valves at said auxiliary turbine to regulate the rate at which fuel gas is delivered to said auxiliary turbine.

2. A power plant as defined in claim 1 wherein said auxiliary turbine is of the single-bearing type to facilitate sealing thereof.

3. A power plant as defined in claim 1 wherein said auxiliary turbine is of the single-bearing type having a single crown impulse rotor.

4. A power plant as defined in claim 1 wherein said auxiliary turbine is of the type having a single crown impulse rotor and a diffuser at the outlet side of said rotor to eifect a drop in gas pressure within the turbine housing below that of atmosphere thereby preventing gas leakage losses at the shaft packing.

5. A power plant as dened in claim 1 and which further includes a heat exchanger in the outlet of said main turbine through which the fuel gas is passed for preheating by the turbine exhaust gases, an auxiliary combustion chamber, means for delivering a portion of the fuel gas to said auxiliary combustion chamber for combustion thereof, and means connecting the outlet of said auxiliary combustion chamber with the outlet of said main turbine so that the combustion gases produced in said auxiliary combustion chamber pass in heat transfer relation with said heat exchanger.

HANS PFENNINGER.

REFERENCES CITED The following references are of record in the file of this patent:

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